The objective of the proposed research is to study the role of specific genes in the regulation of eukaryotic development. These genes can be identified by isolating specific developmental mutants. I have chosen Drosophila for this work, in part, because techniques are already available for extensive genetic analyses of such mutants. But also because the imaginal discs of Feosophila represent a unique developmental system in which the major processes of development, i.e., determination and diffferentiation are separated in time. The idea is to isolate mutants which dramatically alter imaginal disc development and to use these mutants as tools for genetic and biochemical analysis of the steps occurring during normal development. In fact, I have already isolated many such mutants on the third chromosome of Drosophila. To continue this work I am proposing to initiate a search for mutants on the second chromosome which will extend the range of different genes identified. The procedure designed for isolating these new mutants will also screen for temparature-sensitive mutants on either the 2nd or 3rd chromosome. This important class of mutants will be used for timing the action of specific genes during development. The imaginal discs formed in one group of mutants do not differentiate completely. The nature of the defects in these mutants will be classified by comparing the biochemical events which occur with normal vs. mutant discs incubated with moulting hormone in vitro. Mature imaginal disc cells are fully determined for their future development and, in addition, they can transmit their determined state accurately from one cell generation to the next. Specific molecules are likely to be responsible for maintaining the determined state and therefore must be synthesized in each cell generation. Biochemical studies of the nature of these molecules has been limited by the lack of quantities of cells determined for a particular state. I proposed to obtain sufficient material for such studies by developing a method for growing imaginal disc cells in vitro.